We are examining the composition of the oligosaccharide-lipids which are synthesized by the bovine retina, in vitro, and their role as possible precursors of the oligosaccharide chains of rhodopsin. We have observed that the biosynthesis of the N-acetylglucosamine-containing mono, di and tri-saccharide lipids (compounds which are involved in the biosynthesis of the core region of the asparagine-linked glycoproteins) is strongly influenced by GDP-mannose and the cation, magnesium. We are examining the kinetic properties of these reactions. We are investigating in greater detail the characteristics of the rhodopsin-cleaving enzyme which we have detected in the pigment epithelium. Using the RCS rat, we are examining the effect of the retinal dystrophies on this enzymatic reaction.